The study is to assess the extent to which S. mutans, S. sanguis and organisms of the lactobacillus species precede the clinical manifestation of fissure caries. It will also examine, over time the quantitative relationship between these organisms in both clinically sound and in clinically carious teeth. The time sequence of colonization of the organisms, will be related to the development, or absence of development, of clinical caries, and the study will seek to demonstrate microbiological developments that predict the diagnosis of clinical caries with a high degree of probability. This three-year longitudinal study is an epidemiological-microbiological collaboration. The study began with 495 children aged 6-7 in the nonfluoridated community of Coldwater, Michigan, in April 1979. Each child is having samples of dental plaque taken from the occlusal fissures of the mandibular first permanent molars at six-month intervals, and is receiving a dental examination each year. Results of the subsequent bacterial counts are compared with the carious status of the teeth as determined by clinical examinations, and the results from various examination and sampling cycles compared.